1. Field of the Invention
The present invention relates to a lens driving device and an image forming apparatus, and, more specifically to a lens driving device, which enables making a fixed cylinder provided with a cam groove, of a resin, has a high precision of a position of a lens group upon a region where photography may be performed, and prevents a malfunction from arising, such as might be caused by an impact upon the lens driving device, and an image forming apparatus including the lens driving device so configured.
2. Description of the Related Art
In recent years, it is common for a large number of photographic lenses that are employed in various types of cameras to include zoom lenses, which change positions of a plurality of lens groups when a photograph is taken, and thereby sequentially change a focal length of the photography that is performed with the camera that employs the zoom lens. In addition, it becomes mainstream to use a collapsible zoom for the photographic cameras, because these lenses are capable of achieving a greater miniaturization of the camera by collapsing the lens groups within a fixed cylinder of a lens barrel when a photograph is not being taken, and thus narrowing an interval between the respective lens groups when the photograph is not being taken. A mechanism is commonly employed as a moving device, which causes the lens groups to move upon the collapsible zoom lens, which includes a fixed cylinder and a rotational cylinder. The rotational cylinder is installed upon the fixed cylinder, in a cam engagement or helicoid engagement, so as to cause the rotational cylinder to move upon an optical axial direction.
A typical structure of the mechanism described herein includes causing the rotational cylinder to extend and retract in a line with a cam groove, while rotating with respect to the fixed cylinder, supporting a linear guide cylinder upon an interior portion of the rotational cylinder. The linear guide cylinder is capable of rotating relative to the rotational cylinder, and moves in a unified manner with the rotational cylinder upon the optical axial direction, additionally supporting a lens frame upon an interior portion of the straight line guide cylinder. In addition to supporting the lens groups, the lens frame includes a cam follower, such that the cam follower passes through a groove aperture that extends along an optical axial direction of the linear guide cylinder, and which fits with the cam groove that is installed upon the interior surface of the rotational cylinder.
When the rotational cylinder rotates, it is possible for the lens frame and the lens groups that are supported by the lens frame to move upon the optical axial direction in accordance with a cam shape of the cam groove, avoiding being rotated in the process by tracking the groove aperture of the linear guide cylinder. The rotational cylinder and the linear guide configure a structure wherein a rotational key, which is placed upon the straight line guide, and which protrudes upon a radial direction of the straight line guide, and a rotational groove, which is placed upon an interior diameter of the rotational cylinder, are fitted together, such that the linear guide cylinder is capable of the relative rotation between the structure and the rotational cylinder, and of moving in a unified manner with the rotational cylinder upon the optical axial direction.
In general, the fixed cylinder is commonly formed from a resin. Given that the cam groove that is placed upon the fixed cylinder is formed upon an interior diameter side of the fixed cylinder, a mold for forming the cam groove is made into a plurality of segments, and the mold is released from the item thus formed after the formation of the item, a configuration is commonly implemented wherein each respective segmented mold is caused to slide toward a center of the fixed cylinder. A technique is used that causes a latitudinal cross-section of the cam groove to assume a tapering surface with respect to a latitudinal surface, i.e., an axial cross-section, of the fixed cylinder, in order to prevent an undercut by the sliding of the mold upon the fixed cylinder. Given that the mold slides toward a center axial direction of the fixed cylinder, or put another way, toward an interior radial direction side of the fixed cylinder, a site of a fluctuation of the cam groove with respect to the fixed cylinder constitutes a target site for the undercut, and a site whereat the cam groove does not fluctuate is not undercut.
As described herein, the lateral cross-section shape becomes the tapering surface of the cam groove, and it is typical for the cam follower, which fits together with the cam groove that becomes the tapering surface, to comprise a conical shape in order to fit with the taper surface shaped cam groove. By presuming a configuration of the cam groove and the cam follower such as is described herein, it is possible for the rotational cylinder to move with precision upon the optical axial direction, while rotating upon a circumference of the optical axis, with respect to the fixed cylinder. In addition, it is possible to apply a relationship between the cam follower and the cam groove to the lens frame and the rotational cylinder, as described herein, as well as to a cam fitting among the rotational cylinders, in addition to the relationship between the fixed cylinder and the rotational cylinder alone. The cam follower is furthermore not simply restricted to protruding externally, and it would be additionally possible to apply the cam follower so as to protrude internally as well, in like fashion.
A lens barrel, such as is described herein, which is primarily embedded within such as a digital camera, as well as being used in other typical photographic devices, may on occasion incur a powerful impact as a result of such as a fall when the lens barrel is in a picture-taking mode. An exertion of such an impact upon the lens barrel results in a tremendous load being exerted in turn upon the cam follower portion by way of a member that configures the lens barrel. Given that the cam follower portion is fitted at an incline with respect to an axial direction of the lens barrel, the load being exerted upon the axial direction of the lens barrel thus causes a slippage to occur, the rotational cylinder or the fixed cylinder are deformed by being pressed by the cam follower, the cam follower becomes misaligned from the cam groove, and a malfunction may arise.
A variety of structures have been proposed in order to solve the problems described herein. One such structure is a zoom lens barrel disclosed according to Japanese Patent Application Laid Open No. 2003-84185. That is to say, a configuration is described according to Japanese Patent Application Laid Open No. 2003-84185 comprising a first frame member, further comprising a first cam groove and a second cam groove, and a second frame member, further comprising a first cam follower and a second cam follower, and which is capable of extending and retracting with respect to the first frame member. The first cam groove and the second cam groove of the configuration described according to Japanese Patent Application Laid Open No. 2003-84185 further comprise a partition portion that is formed from a taper portion, which inclines at a prescribed quantity with respect to the optical axis, with respect to a first region that extends upon a circumference direction of the first frame member, and a vertical portion that is formed in a vertical direction upon the optical axis, and further comprise a partition portion that is formed solely from the taper portion that inclines at the prescribed quantity with respect to the optical axis, with respect to a second region that differs from the first region. When the second frame member extends and retracts relative to the first frame member, either the first cam follower or the second cam follower, at a minimum, is fitted at all times with either the first cam groove or the second cam groove, upon an entirety within a range of movement of the second frame member relative to the first frame member, and an external force that acts upon the second frame member is received with the vertical portion of the cam groove.
Given such a configuration as is described herein, two cam followers are required to mutually regulate a relative positional relationship between the two frame members, and the requirement of the two cam followers results in an increase in a quantity of components and an enlargement of a space required to house the components. Furthermore, if the respective positions of the two cam followers are even slightly flawed in their precision, either a compression force or a pulling force will be exerted between the two cam grooves by the two cam followers. As a result, it is necessary to exert a tremendous quantity of force in order to cause the configuration to operate, which is a factor that gives rise to a malfunction.
Japanese Patent Application Laid Open No. 2002-90611 similarly discloses a lens barrel that approximates the invention disclosed according to Japanese Patent Application Laid Open No. 2003-84185. The invention disclosed according to Japanese Patent Application Laid Open No. 2002-90611 differs from the invention disclosed according to invention 2003-84185 in that one cam follower of the two cam followers is treated as a runner, and the runner is fitted upon a planar portion. Similar to the invention disclosed according to Japanese Patent Application Laid Open No. 2003-84185, the invention disclosed according to Japanese Patent Application Laid Open No. 2002-90611 incurs an increase in a quantity of components and an enlargement of a space required to house the components, and also demands a high degree of precision, respectively, of each of the two cam followers.
In addition, Japanese Patent No. 4070351 discloses an optical device, comprising a collapsible lens barrel, which further comprises a cam groove, which is shaped in a latitudinal cross section tapering shape, and a cam follower, which is conically shaped, and which is fitted with the cam groove. Placing a guide partition upon a position corresponding to aft of the optical axial direction of the cam follower, which is guided by a component further corresponding to a state of extension by the cam groove, such that the guide partition comes into contact with the cam follower, causes an impact to be absorbed by the guide partition.
All of the cited patent application references described herein respectively disclose forming the latitudinal cross section shape of the cam groove into the tapering shape, and forming the cam follower that fits with the cam groove into the conical shape, in order to facilitate manufacturing the conical shaped member that comprises the cam groove with a unified resin formation. The relationship of the fitting of the cam groove, which is shaped in the latitudinal cross section shaped tapering shape, with the conically shaped cam follower, is susceptible to coming undone by an impact being exerted upon the fitting of the cam groove with the cam follower, and thus, all of the cited patent application references are configured such that either a) an external force acting upon the fitting of the cam groove with the cam follower is absorbed by the vertical portion of the cam groove, or b) an impact is absorbed by a guide partition, which is installed upon a position that corresponds to the aft of the cam follower in the optical axial direction.
As described herein, however, according to the invention disclosed according to Japanese Patent Application Laid Open No. 2003-84185 and the invention disclosed according to Japanese Patent Application Laid Open No. 2002-90611, two cam followers are required to regulate the relative positional relationship between the two respective frame members, resulting in an increase in the number of components and a greater space required for the configurations. A further problem is that if the respective positions of the two cam followers are even slightly flawed in their precision, it is necessary to exert a tremendous quantity of force in order to cause the configuration to operate, which may easily provide a factor that gives rise to a malfunction.
In addition, according to the invention disclosed according to Japanese Patent No. 4070351, the impact that is exerted upon the configuration from an external source is absorbed solely by a guide partition, which is placed upon a position corresponding to aft of the optical axial direction of the cam follower, which in turn is guided by a component corresponding to a state of extension by the cam groove, such that the guide partition comes into contact with the cam follower. A concept that the guide partition constitutes a portion of a configuration that is intended to increase the precision of the lens position is not present with the invention disclosed according to Japanese Patent No. 4070351.